SUMMARY
This paper proposes a set of novel indices for evaluating the kinematic performance of a 3-
R
RS (R and S denote revolute and spherical joint respectively,
R
denotes active joint.), parallel ...mechanism whose translational and rotational movements are strongly coupled. First, the indices are formulated using the decoupled overall Jacobian matrix, which is developed using coordinate transformation. Then, the influences of the homogeneous dimensionless parameters on these indices are investigated. In addition, the dimension synthesis of the 3-
R
RS parallel mechanism is carried out by minimizing the mean value of the kinematic performance indices and their standard deviation. The results demonstrate that the established approach facilitates good global kinematic performance of the parallel mechanism.
•A transmission index for kinematic evaluation of parallel manipulators is proposed.•The index is based on the pressure angles and kinematically equivalent mechanism.•Kinematically equivalent ...mechanism is constructed based on the force transmission.•The first index involves the width of revolute joint in the kinematic design.
In this paper, we present a new transmission index (TI) for kinematic performance evaluation of a class of parallel manipulators with a 3-RS (or 3-SR) structure; termed the primary structure obtained by locking all actuated joints in the manipulators. TI is based on the pressure angle that is defined in a kinematically equivalent structure, a 6-SS structure by replacing an RS chain of the primary structure with a pair of SS chains, which can reflect the practical force transmission and constraint characteristics of R joint composed of two bearings in the original manipulator. The effectiveness of TI is verified by considering 3-PRS and 3-RPS parallel manipulators. The singularity analysis, relationships between the maximum joint forces and index values, distribution of TI inside the workspace, and an application of TI to a kinematic design are demonstrated. The proposed approach can indicate both output and constraint singularity conditions with a single index, can be achieved by simple calculation process without complicated normalization, and can include the width of the revolute joint in the kinematic performance evaluation of this class of parallel manipulators.
The application of the stereoscopic parking robot makes it possible to relieve the pressure of urban traffic efficiently. With the aggravation of energy and environmental problems, the energy ...consumption of the stereoscopic parking robot is mainly concerned. In robot design, the kinematic performance reflects the motion transfer capability of the mechanism. A reasonable size of the mechanism can make energy transfer more efficient. This paper proposes a 2-DOF (Degree of Freedom) parallel lifting mechanism of the stereoscopic parking robot. Its branch contains double-constrained triangles that can perform symmetrical movements. Forward kinematics, inverse kinematics, workspace, and singular configuration are studied and analyzed. In this scheme, depending on the characteristics of the mechanism, the evaluation indices of motion consistency, workspace, and singularity performance are proposed. The energy-saving optimization design method based on the multiple kinematic performance indexes is used to find the optimum combination of structural parameters in the feasible region. Finally, the parallel lifting mechanism prototype is constructed, and the dynamic verification experiments are performed at driving speeds of 15.625, 12.5, and 10.42 mm/s. The results provide helpful guidance for the choice of driving speed to achieve optimal movement transfer capacity and stability of the mechanism. The multiple performance index design method can also be applied to other parallel mechanisms with low mobility, which require energy savings and steady motion.
Performing the machining of complex surfaces can be a challenging task for a robot, especially in terms of collaborative robotics, where the available motion capabilities are greatly reduced in ...comparison with conventional industrial robot arms. It is necessary to evaluate these capabilities prior to task execution, for which we need efficient algorithms, especially in the case of flexible robot applications. To provide accurate and physically consistent information about the maximum kinematic capabilities while considering the requirements of the task, an approach called the Decomposed Twist Feasibility (DTF) method is proposed in this study. The evaluation of the maximum feasible end-effector velocity is based on the idea of decomposition into the linear and angular motion capabilities, considering a typical robot machining task with synchronous linear and angular motion. The proposed DTF method is presented by the well-known manipulability polytope concept. Unlike the existing methods that estimate the kinematic performance capabilities in arbitrarily weighted twist space, or separately in the translation and the rotation subspace, our approach offers an accurate and simple solution for the determination of the total kinematic performance capabilities, which is often highly required, especially in the case of robot machining tasks. The numerical results obtained in this study show the effectiveness of the proposed approach. Moreover, the proposed DTF method could represent suitable kinematic performance criteria for the optimal placement of predefined tasks within the robot workspace.
In this article, our recent work on a kind of 2-degree-of-freedom lower-mobility parallel mechanism, which has one rotation degree of freedom and one translational degree of freedom, used in ...multilayer garage is presented. It has the following characteristics: lower-mobility, non-symmetric structure but can realize symmetric movement and a good compatibility for different kinds of lifting work. Kinematic performance should be considered in the first of designing a new kind of mechanism, the optimal kinematic design and analysis of this lower-mobility parallel mechanism are primarily investigated. In process of study, the global conditioning index over workspace is adopted, we establish a new evaluation method for the lower-mobility parallel mechanism, called global symmetry index and simulation results are shown. In addition, the flexible workspace of this lower-mobility parallel mechanism is also proposed. The evaluation index can be also applied on other lower-mobility parallel mechanism, which needs steady and symmetric movement.
Performance evaluation of a parallel robot is a multicriteria problem. By taking Delta robot as an object of study, this paper presents the kinematic performance evaluation of a three translational ...degrees-of-freedom parallel robot from the viewpoint of singularity, isotropy, and velocity transmission. It is shown that the determinant of a Jacobian matrix cannot measure the distance from the singular configuration due to the existing inverse kinematic singularity of a Delta robot. The determinants of inverse and direct kinematic Jacobian matrices are adopted for the measurement of distance from the singular configuration based on the theory of numerical linear dependence. The denominator of the Jacobian matrix will be lost in the computation of the condition number when the end-effector is on the centerline of the workspace, so the Delta robot may also be nearly at a singular configuration when the condition number of the Jacobian matrix is equal to 1. The velocity transmission index whose physical meaning is the maximum input angular velocity when the end-effector translates in the unit velocity is presented. The evaluation of singularity, isotropy, and velocity transmission of a Delta robot is investigated by simulation. The velocity transmission index can also be used for the velocity transmission evaluation of a parallel robot with pure rotational degrees-of-freedom based on the principle of similarity. The physical meaning is modified to be the maximum input velocity when the end-effector rotates in the unit angular velocity.
This paper deals with the conceptual design and kinematics of a new asymmetrical parallel mechanism, named "TAM". The robot is a modified version of the SKM400 concept, achieved by integrating one of ...the three active limbs into the passive limb. The idea leading to the innovation of the parallel mechanism is systematically addressed. The condition number of the Jacobian is used to evaluate the kinematic performance. It has been concluded that the proposed mechanism is cost effective and competitive in terms of theoretical kinematic performance in comparison with the SKM400.
Kinematics research of mechanism is very important, the dynamic analysis and the design are based on kinematical analysis. In this paper, a novel robot shoulder joint based on 3-RRR orthogonal ...spherical parallel mechanism is proposed, and the kinematics transmission equation of shoulder joint is derived by using the kinematics inverse solution, and Jacobin matrix is established. Then Jacobin matrix is introduced into the global performance index, and the velocity of global performance evaluation index is defined. Furthermore, the shoulder joint dimensions are changed, and the global performance index is analyzed, then a performance atlas is given at the work spaces of shoulder joint with different dimension. It is found that the Jacobin matrix has more important influence on the kinematics performance of the shoulder joint. Having a good kinematics performance, structure dimensions ranges of shoulder joint are gained, thus the evaluation of kinematics of shoulder joint is more comprehensive. Finally, a novel robot shoulder joint is designed with the kinematics performance evaluation index.
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